numpy.
triu
Upper triangle of an array.
Return a copy of an array with the elements below the k-th diagonal zeroed.
Please refer to the documentation for tril for further details.
tril
See also
lower triangle of an array
Examples
>>> np.triu([[1,2,3],[4,5,6],[7,8,9],[10,11,12]], -1) array([[ 1, 2, 3], [ 4, 5, 6], [ 0, 8, 9], [ 0, 0, 12]])